The invention relates to the field of vision testing and, in particular, to a color vision deficiency test using a computer display.
For a number of testing situations, such as remote testing over the Internet, the main challenge is to develop a color vision deficiency test that can provide meaningful assessment in spite of the degradations inherent in uncalibrated and otherwise unknown display devices. Often, performance on psychophysical tests can improve when device miscalibrations lead to artifacts that provide additional cues for the correct target, resulting in a higher false negative rate for detecting sensory deficiencies, meaning that color deficient observers are inappropriately categorized as not having color vision deficiencies. By designing the presentation so that limitations in the display increase the false alarm rate (instead of the false negative rate), a more conservative measure of performance is achieved. The benefit for a screening evaluation is that it is less likely that a person having a sensory deficit will be overlooked, i.e., more people in need of attention will be directed to the appropriate clinicians.
Colors can be described by coordinates in a three-dimensional color space; an example of this is the RGB triplet used to specify colors on a computer monitor. Color vision deficiencies can be characterized by confusion lines in a color space, wherein two colors lying on such a line are difficult or impossible to discriminate from each other by a color deficient observer. Many tests of color vision exploit this phenomenon, and their reliability hinge on the precision with which test colors can be specified. However, if one has only limited control of monitor calibration, as is the case when testing over the Internet, colors displayed at a remote location generally do not render as specified. Color deficient observers could thus pass the test if colors do not fall on a confusion line, which is a disastrous failure mode and one of the main reasons color vision assessment is not generally feasible outside a carefully controlled clinical setting.
There are three major types of color vision deficiencies: protanopia, deuteranopia, and tritanopia, corresponding to an absence or malfunctioning of long, medium, and short wavelength-sensitive cone photoreceptors, respectively. Subcategories of color vision deficiency are the “anomalous” versions of each of the three major categories. The three major categories are characterized by the inability to discriminate colors along particular confusion lines in color space. Anomalies are characterized by greater difficulty, as compared to color normal observers, in discriminating colors along similar confusion lines as the corresponding major deficiencies. Each major type of color vision deficiency requires a test series tailored to its unique set of confusion lines. Each major type of color vision deficiency requires a test series.